1. Field of the Invention
The present invention relates generally to digital television receivers and other types of host devices for processing video or other multimedia information, and more particularly to techniques for providing interaction between removable cards and such host devices.
2. Description of the Related Art
Communication between applications running on physically separate devices is becoming increasingly important as a result of ongoing development in areas such as end-to-end digital communication systems and Internet applications. Robust, flexible and simple inter-application communication mechanisms are desirable in that such mechanisms allow application developers to shorten the time-to-market of products. Examples of existing technologies that have been designed to support inter-application communication include Common Object Request Broker Architecture (CORBA), Distributed Component Object Modeland (DCOM), Java Remote Method Invocation (RMI), and the Sun Microsystems Java-based system known as JINI for networking home appliances, desktop computers and other types of consumer electronics. The particular technology selected will generally depend on factors such as the type of applications and system architecture involved.
One area in which inter-application communication is particularly important is in digital television (DTV) systems. The trend in such systems is to separate the DTV functions into two categories: (1) the standardized functions, such as MPEG-2 transport stream demultiplexing and decoding; and (2) proprietary and security-related functions, such as conditional access systems and proprietary applications. The standard functions can then be implemented on a DTV receiver host, and the proprietary and security-related functions can be implemented on a removable card that is inserted into and communicates with the host. The host and removable card interact to provide desired programs and/or services to consumers.
This type of card-host system architecture increases the reusability and extensibility of the DTV receiver. For example, a consumer is able to purchase a DTV receiver in the form of a set-top box that includes a set of standard features. If the consumer then wants to receive premium programs and/or services from a cable operator, the consumer can purchase or lease a removable card from the cable operator or other source. The removable card in this case contains all of the functions needed to allow the consumer to receive and decrypt the premium programs and/or services provided by the cable operator. In the event that the cable operator adopts new technologies or provides new programs and/or services, the operator can upgrade the removable card, e.g., through a software download or replacement. Alternatively, if the consumer chooses to subscribe to a different cable operator, the consumer can return the removable card to the original operator, and purchase or lease a removable card from the new operator. In any case, the investment of the consumer in the DTV receiver is protected without compromising the ability of the consumer to take advantage of new technologies, programs and/or services.
Another advantage of the above-described card-host system architecture is that it protects the intellectual property rights of content and service providers against hackers who may try to break the system and “steal” the premium programs and/or services. This is due to the fact that all of the proprietary and security-related functions are in a separate removable card that can be disabled and/or replaced if a hacking attempt is detected.
In order for the card-host system architecture to work properly, the host and the removable card must establish a communication channel and protocol. In conventional systems, the host and card typically communicate through message passing, based on a defined set of data descriptors and/or structures. For example, if a consumer wants to order a video on demand (VOD) service, he or she sends a request through a user interface to the host, and the host in response sends a “VOD requested” data descriptor to the removable card. In such an arrangement, the removable card may then respond by sending a data descriptor that contains the requested list of VODs with the information necessary for ordering.
There are a number of significant drawbacks to the conventional card-host communication described above. First, the data descriptors generally must be standardized, such that the hosts and removable cards, which are usually manufactured by different vendors, can understand each other. However, it is often very difficult to specify standardized “generic” data descriptors that will satisfy all of the venders, users and other involved parties. Even if such a descriptor is found that appears acceptable and complete at the time it is defined, as new business needs emerge, it may become necessary to add or to remove some items in an existing data descriptor or add a new data descriptor. In such situations, the parties involved are forced to either change an existing standard or do without the desired change. Another significant drawback is that the published details regarding data descriptors may reveal information regarding the inner structure of the removable card, or other information that could be used by hackers to break the system.
Other techniques have been developed for implementing card-host communications. For example, U.S. Pat. No. 5,588,146 describes a system in which a removable card stores software programs with rights of access. The software can be downloaded into a microcomputer after the card is inserted therein. U.S. Pat. No. 5,739,510 describes the interaction between a removable card and a “dumb” terminal that handles user interface operations including input and output. The card performs application-specific operations, and the results are then communicated with the terminal. Another known technique, described in U.S. Pat. No. 5,844,218, relates to a removable card that stores customized information for television receivers, such that different consumers can receive different services bases on the information stored on their cards.
Unfortunately, these and other known techniques have failed to provide an acceptable solution to the above-described problem of inter-application communication in a card-host architecture. A need therefore exists for improved techniques for implementing communications between a removable card and a host device in a DTV system or other system based on a card-host system architecture.